Beg English knight to negotiate (7)
I believe the answer is:
entreat
'beg' is the definition.
(thesaurus)
'english knight to negotiate' is the wordplay.
'english' becomes 'e' (abbreviation).
'knight' becomes 'n' (chess).
'to negotiate' becomes 'treat' (I've seen this before).
'e'+'n'+'treat'='ENTREAT'
(Other definitions for entreat that I've seen before include "Sue" , "Beg earnestly, appeal" , "Beg earnestly, beseech" , "go begging?" , "Ask (someone) anxiously" .)